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Blood, 15 December 2006, Vol. 108, No. 13, pp. 4118-4125. Prepublished online as a Blood First Edition Paper on August 10, 2006; DOI 10.1182/blood-2006-03-006700.
IMMUNOBIOLOGY The tryptophan catabolite L-kynurenine inhibits the surface expression of NKp46- and NKG2D-activating receptors and regulates NK-cell functionFrom the DIMES (Dipartimento di Medicina Sperimentale), Università di Genova, Genova, Italy; IST (Istituto Nazionale per la Ricerca sul Cancro), Genova, Italy; Istituto Giannina Gaslini Genova-Quarto, Genova, Italy; and Centro di Eccellenza per la Ricerca Biomedica Genova, Genova, Italy.
Tryptophan (Trp) catabolism mediated by indoleamine 2,3-dioxygenase (IDO) plays a central role in the regulation of T-cellmediated immune responses. In this study, we also demonstrate that natural killer (NK)cell function can be influenced by IDO. Indeed, L-kynurenine, a Trp-derived catabolite resulting from IDO activity, was found to prevent the cytokine-mediated up-regulation of the expression and function of specific triggering receptors responsible for the induction of NK-cellmediated killing. The effect of L-kynurenine appears to be restricted to NKp46 and NKG2D, while it does not affect other surface receptors such as NKp30 or CD16. As a consequence, L-kynureninetreated NK cells display impaired ability to kill target cells recognized via NKp46 and NKG2D. Instead, they maintain the ability to kill targets, such as dendritic cells (DCs), that are mainly recognized via the NKp30 receptor. The effect of L-kynurenine, which is effective at both the transcriptional and the protein level, can be reverted, since NK cells were found to recover their functional competence after washing.
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